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  • Title: Comparative investigation by two analytical approaches of enthalpy relaxation for glassy glucose, sucrose, maltose, and trehalose.
    Author: Kawai K, Hagiwara T, Takai R, Suzuki T.
    Journal: Pharm Res; 2005 Mar; 22(3):490-5. PubMed ID: 15835755.
    Abstract:
    PURPOSE: In an effort to understand the stability of glassy sugars such as glucose, sucrose, maltose, and trehalose, the molecular mobility below the glass transition temperature (Tg) was investigated by an enthalpy relaxation measurement with differential scanning calorimetry (DSC). METHODS: The glassy sample was aged over several days at (Tg - 10) K to (Tg - 30) K, before a DSC heating scan was taken. The relaxed enthalpy (deltaHrelax) was estimated from the endothermic peak area. The enthalpy relaxation time was analyzed from the time course of deltaHrelax using two different approaches; Kohlrausch-Williams-Watts (KWW) and extended Adam-Gibbs (exAG). RESULTS: TauKWW, which is defined as the mean average enthalpy relaxation time in a distribution, and tau(eff)0 and tau(eff)infinity, which correspond to the enthalpy relaxation time of the initial minimum and final maximum cooperative rearrangement region, were estimated by KWW and exAG, respectively. And three activation energies for enthalpy relaxation were calculated from the Arrhenius plot. CONCLUSIONS: Although these deltaEs originated from different theoretical backgrounds, almost the same trend was observed for a comparison of the values of the four sugars. The finding that the deltaEs of glassy trehalose were the largest among the four sugars may support the reason that glassy trehalose is an effective stabilizer.
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